Cloud computing is relatively a new computing technique and it became very popular recently. It refers to both applications which are delivered as services through the Internet as well as resources (software and hardware) in the data centers. Usually the resources in the data centers are called as Cloud. Cloud computing leverages Virtualization Technology which makes it possible to have each node appear as separate physical machine allowing user to load custom software and operating system on each node and configure custom rules for each node. Cloud computing makes several distributed computers connected together to form a big logical computer which can handle large amount of data and computation.
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We can say that Cloud Computing is the combination of earlier computing techniques such as parallel computing, distributed computing and grid computing. It is an emerging field of computer science. It’s called Cloud computing because the data and applications exist on a “cloud” of Web servers. To simplify the concept, Cloud computing can be defined as simply the sharing and use of applications and resources of a network environment to get work done without concern about ownership and management of the network’s resources and applications. With Cloud computing, computer resources for getting work done and their data are no longer stored on one’s personal computer, but are hosted elsewhere to be made accessible in any location and at any time.
Client-server computing is a distributed computing model. In this model the client applications request services from server processes. Clients and servers typically run on different computers interconnected by a computer network. When you retrieve information from the World Wide Web through Internet, you are actually using client-server computing. However, the term client-server computing is generally applied to systems in which an organization runs programs with multiple components distributed among computers in a network. The concept is frequently associated with enterprise computing, which makes the computing resources of an organization available to every part of its operation. A client application is a process or program that sends messages to a server via the network. Those messages request the server to perform a specific task, such as looking up a customer record in a database or returning a portion of a file on the server’s hard disk. The client manages local resources such as a display, keyboard, local disks, and other peripherals. The server process or program listens for client requests that are transmitted via the network. Servers receive those requests and perform actions such as database queries and reading files. Server processes typically run on powerful PCs, workstations or mainframe computers (Figure 12.1).
An example of a client-server system is a banking application that allows a clerk to access account information on a central database server. All access is done via a PC client that provides a graphical user interface (GUI). An account number can be entered into the GUI along with how much money is to be withdrawn or deposited, respectively. The PC client validates the data provided by the clerk, transmits the data to the database server, and displays the results that are returned by the server.
The client-server model is an extension of the object-based (or modular) programming model, where large pieces of software are structured into smaller components that have well defined interfaces. This decentralized approach helps to make complex programs maintainable and extensible. Components interact by exchanging messages or by Remote Procedure Calling (RPC). The calling component becomes the client and the called component the server.
A client-server environment may use a variety of operating systems and hardware from multiple vendors. Vendor independence and freedom of choice are further advantages of the model. For example, inexpensive PC equipment can be interconnected with mainframe servers, for example.
It is very easy to scale up client-server systems since server functions can be distributed across more and more server computers as the number of clients increase. Server processes can thus run in parallel, each process serving its own set of clients. However, when there are multiple servers that update information, there must be some coordination mechanism to avoid inconsistencies.
In structured peer-to-peer networks, peers (and, sometimes, resources) are organized following specific criteria and algorithms, which lead to overlays with specific topologies and properties. Unstructured peer-to-peer networks do not provide any algorithm for organization or optimization of network connections. In particular, three models of unstructured architecture are defined. In pure peer-to-peer systems the entire network consists solely of equipotent peers. There is only one routing layer, as there are no preferred nodes with any special infrastructure function. Hybrid peer-to-peer systems allow such infrastructure nodes to exist often called super-nodes. In centralized peer-to-peer systems, a central server is used for indexing functions and to bootstrap the entire system. Although this has similarities with a structured architecture, the connections between peers are not determined by any algorithm. The first prominent and popular peer-to-peer file sharing system, Napster, was an example of the centralized model. Gnutella and Freenet, on the other hand, are examples of the decentralized model. Kazaa is an example of the hybrid model.
Collaborative computing refers to the distributive computing technology which supports collaboration or helps people to exchange information mutually. In collaborative computing, a complete sharing of applications takes place enabling the use of collaborative resources. Also called as group ware, collaborative computing allows the team spread geographically to develop or use a common database. With such a kind of innovative technology, the concept of team-work has acquired a new meaning.
No doubt that collaborative computing is the future of almost all the organizations as it is set to remodel the working styles. But, till today, its use is limited in organizations. More so, the collaborative computing has been mainly found to be useful in SMBs (Small & Medium Businesses). All the information from financial to marketing to any other data can be stored and shared by collaborative computing. This kind of computing is giving rise to a less hierarchical organization while pushing the organization towards a more flat side. The need for collaborative computing arises from the fact that every time all the physical resources cannot be in one place. In collaborative computing, every organization’s LAN (Local Area Network) servers are connected via WAN (Wide Area Network). This technology enables thousands of users to connect to the network.
Now let’s focus our attention to the main theme of this chapter i.e. Cloud Computing. Cloud computing is an IT computing style that delivers IT services (infrastructure, software, data store and information) in a simplified way to end users over internet (Figure 12.4). So how it is different from existing models? Well. The fundamental differences are how these services (infrastructure, software, data store and information) are provided and how they are accessed by users. A most common example is Google Apps which provides web based office tools to end users. So you just need a web browser to access the office suite of applications, where you can create, save, share documents online, without installing any dedicated software (office tools) on your computer. This is an example of Software as a Service cloud offering.
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In general, Cloud computing uses information technology as a service over the network. The concept generally encompasses of Infrastructure as a Service (IaaS), Platform as a Service (PaaS), Hardware as a Service (HaaS) and Software as a Service (SaaS). Cloud Computing has the ability to rent a server or servers and run a geophysical modeling application available anywhere. It can be able to rent a virtual server, load software on it, turn it on and off at will, or clone it to meet a sudden workload demand. It can store and secure large amounts of data that is accessible only by authorized applications and users. It is supported by a cloud provider that sets up a platform with the ability to scale automatically in response to changing workloads. It can use a storage cloud to hold application, business, and personal data. And it has the ability to use a handful of Web services to integrate photos, maps, and GPS information to create a front page in customer Web browsers.
Distributed computing refers to the computing model in which individual computers are physically distributed within some geographical area. A distributed system consists of multiple autonomous computers. The computers interact with each other in order to achieve a common goal. (Refer section 12.2.3)
Collaborative computing refers to the distributive computing technology which supports collaboration or helps people to exchange information mutually. In collaborative computing, a complete sharing of applications takes place enabling the use of collaborative resources. Also called as group ware, collaborative computing allows the team spread geographically to develop or use a common database. (Refer section 12.2.4)
In general, Cloud computing uses information technology as a service over the network. The concept generally encompasses of Infrastructure as a Service (IaaS), Platform as a Service (PaaS), Hardware as a Service (HaaS) and Software as a Service (SaaS). (Refer section 12.3)
Virtualization Technology and Service Oriented Architecture (SOA) are the two key characteristics of Cloud Computing. (Refer section 12.3.1)
Cloud computing can describe services being provided at any of the traditional layers from hardware to applications. In practice, cloud service providers offer services that can be grouped into several architectural layers and sometimes refer as styles in Cloud Computing environment such as Infrastructure as a Service (IaaS), Platform as a Sservice (PaaS) and Software as a service (SaaS). (Refer section 12.3.2)
While security environment of Cloud Computing is uncertain and declared as unsecured environments, organizations like CSA work diligently on defining the standards, describing best practices, and highlighting the top risks and threats. There were seven threats of Cloud Computing security according to the report published by CSA. (Refer section 12.3.4)
Google, NetSuite, Taleo, Concur Technologies and IBM Lotus Live are some of the Cloud Computing companies that provide Software as a Service (Saas) to their customers. Their services include Email, Word Processing, Calendar, Payroll, HR, and CRM. These companies charge their customers a subscription fee and in return host software on central servers that are accessed by the end users via the internet. (Refer section 12.3.5)
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